The invention relates to an exhaust gas sampling system, and more particularly, the invention relates to a diesel particulate sampling system.
Diesel circulate sampling systems are used to measure particulate matter in the diesel exhaust gas. Raw exhaust is collected from the tailpipe with a probe arranged with the tailpipe. The raw exhaust gas is typically diluted with a dilution gas, homogeneously mixed, and collected by a filter for subsequent measurement. A constant dilution ratio must be maintained so that the quantity of exhaust gas is known when measuring the particulate matter to accurately determine the particulate matter concentration in the exhaust gas.
It may be desirable to utilize a shorter probe for a diesel particulate sampler to provide more accurate detection and measurement of particular matter. Utilizing a significantly shorter probe than the prior art may cause the sampler to be more sensitive to flow and pressure fluctuations present in the tailpipe. Internal combustion engines cause cyclic exhaust fluctuations as the engine pistons reciprocate and exhaust valves open. During a pressure drop, sample exhaust gas and dilution gas may be undesirably drawn out of the probe and back into the tailpipe, thereby changing the dilution ratio in an uncontrolled manner. The portion of the probe with the tailpipe may be lengthened to minimize the effects of the pressure fluctuations. However, the remaining effects of the pressure fluctuations may be undesirable in that the changes in dilution ratio are still unacceptable. As a result, it may be desirable to actively apply pressure pulses within the sampler to cancel pressure pulses from the tailpipe in order to use shorter probes.
The present invention provides a particulate sampler for conveying exhaust gas from exhaust gas source to analysis equipment. The particulate sampler includes a probe for receiving the exhaust gas and a transfer tube for conveying the exhaust gas from a tailpipe to a mixer. The mixer mixes the exhaust gas and a dilution gas from a dilution source. A dilution tunnel mixes and conveys the exhaust gas and dilution gas from the mixer to analysis equipment such as a filter or gas analyzers. A flow pulsation cancellation device includes an actuator in communication with at least one of the tailpipe, probe, transfer tube, mixer, and dilution tunnel for introducing a canceling pressure pulse to minimize the effects of pressures pulses present from the tailpipe within the sampler. The actuator may be a moveable membrane or a fluid flow control valve. Pressure sensors are used to measure the pressure of the undiluted and diluted exhaust gas, and a controller determines the desired canceling pressure pulse based upon the measured pressures.
Accordingly, the above invention provides a device that actively applies pressure pulses within the sampler of a nature sufficient to cancel the pressure pulses from the tailpipe